Wireless communication systems are widely deployed to provide various types of communication such as voice and data. These systems may be based on code division multiple access (CDMA), time division multiple access (TDMA), or some other modulation techniques. A CDMA system provides certain advantages over other types of systems, including increased system capacity.
A CDMA system may be designed to support one or more CDMA standards such as (1) the “TIA/EIA-95-B Mobile Station-Base Station Compatibility Standard for Wideband Spread Spectrum Cellular System” (the IS-95 standard), (2) the standard offered by a consortium named “3rd Generation Partnership Project” (3GPP) and embodied in a set of documents including Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214 (the W-CDMA standard), (3) the standard offered by a consortium named “3rd Generation Partnership Project 2” (3GPP2) and embodied in a set of documents including “C.S0002-A Physical Layer Standard for cdma2000 Spread Spectrum Systems,” the “C.S0005-A Upper Layer (Layer 3) Signaling Standard for cdma2000 Spread Spectrum Systems,” and the “C.S0024 cdma2000 High Rate Packet Data Air Interface Specification” (the cdma2000 standard), and (4) some other standards. Non-CDMA systems include the AMPS and GSM systems.
In a CDMA system, the total available transmit power is allocated among the various users in the system. Therefore, system capacity is constrained by the amount of power transmitted to each user. Various power control techniques are known in the art and are used to reduce or limit the amount of power used by each user, thus increasing overall system capacity
In a modern communication system, such as the W-CDMA system, various channels are multiplexed together and transmitted on a single physical channel. The exemplary W-CDMA system supports data transmission on one or more transport channels. One or more transport formats may be used for each transport channel. Each transport format defines various processing parameters such as the transmission time interval (TTI) over which the transport format applies, the size of each transport block of data, the number of transport blocks within each TTI, the coding scheme to be used for the TTI, and so on. The use of multiple transport formats allows different types or rates of data to be transmitted over a single transport channel. The transport channels can be multiplexed and transmitted on a single physical channel.
A power control mechanism for improving system performance and capacity for such multiple format systems is disclosed in co-pending U.S. Pat. No. 6,983,166, entitled “POWER CONTROL FOR A CHANNEL WITH MULTIPLE FORMATS IN A COMMUNICATION SYSTEM”, issued on Jan. 3, 2006, assigned to the assignee of the present invention and incorporated by reference herein (hereinafter the '604 application).
It is also common in modern communication systems for various other channels to be transmitted in parallel with a physical channel using a common air link. Under certain circumstances, the channels may interfere with each other. For example, in the W-CDMA system, the sync channel is not constrained to be orthogonal to the other physical channels, and so may introduce interference to those channels. Various techniques for mitigating the effects of this type of interference are disclosed in co-pending U.S. Pat. No. 7,292,552, issued on Nov. 6, 2007, entitled “METHOD AND APPARATUS FOR REDUCING INTERFERENCE IN A WIRELESS COMMUNICATION SYSTEM”, U.S. Pat. No. 7,035,284, issued on Apr. 25, 2006, entitled “METHOD AND APPARATUS FOR REDUCING INTER-CHANNEL INTERFERENCE IN A WIRELESS COMMUNICATION SYSTEM EMPLOYING A entitled “METHOD AND APPARATUS FOR REDUCING INTER-CHANNEL INTERFERENCE IN A WIRELESS COMMUNICATION SYSTEM”, all assigned to the assignee of the present invention and incorporated by reference herein (hereinafter the '691 applications).
Power control can be used to overcome interference in certain situations, but not all transport channels or formats are necessarily suitable for power control. Increasing power for each frame, or the portion of each frame experiencing interference, is another alternative to overcome the interference. However, doing so may unnecessarily increase transmit power, thus reducing system capacity. There is therefore a need in the art for reducing interference with a multiple format channel in a communication system.